Method of controlling the polymerization of acrylates

ABSTRACT

The present invention relates to a method of controlling the polymerization of acrylates using a catalyst which is selected from at least one of zinc, cadmium, or mercury halides in combination with free iodine to give acrylate polymers having narrow molecular weight distributions, via group transfer polymerization.

FIELD OF THE INVENTION

The present invention relates to a novel method of controlling thepolymerization of acrylates using a novel catalyst.

Specifically, the present invention relates to a method of controllingthe polymerization of acrylates using a catalyst which is selected fromat least one of zinc, cadmium, or mercury halides in combination withfree iodine to give acrylate polymers having narrow molecular weightdistributions, via group transfer polymerization. The catalysts used inthe instant invention allow for the control of the polymerization toafford such polymers.

BACKGROUND OF THE INVENTION

Group transfer polymerization of acrylates is widely recognized as beingcapable of producing living polymers with controlled molecular weightand narrow molecular weight distribution and there are multiplepublications setting forth such methods. The method generally includesthe reacting of acrylic monomers, or mixtures of them, with initiatorsand a catalyst to obtain living polymers.

For example, in U.S. Pat. No. 4,414,372, issued Nov. 8, 1983 to Farnham,et al, there is disclosed the primary elements of a method to produceliving polymers. The catalysts set forth in that patent for use in themethod include co-catalysts which are a source of bifluoride ions HF2,to produce the polymers.

Preferred are the co-catalysts which include sources of fluoride,cyanide or azide ions, those suitable being Lewis acids, for examplezinc chloride, bromide or iodide, boron triflouride, alkylaluminum oxideand alkylaluminum chlorides.

Most preferred catalysts are tris(dimethylamino)sulfonium biflouride,tetraalkylammonium bifluorides, tetraarylphosphonium bifluorides,bifluorides of the alkali metals, especially potassium, and ammoniumbifluoride.

Another example of disclosure of a method can be found in U.S. Pat. No.4,417,034, which issued Nov. 22, 1983 to Webster in which livingpolymers and their preparation from acrylic-type or maleimide monomersand organosilicon, tin or germanium initiators is shown. The disclosurein that patent relating to catalysts is nearly analogous to that of the'372 patent and does not bear repeating herein.

There is disclosed in U.S. Pat. No. 4,508,880, which issued Apr. 2, 1985to Webster, the further preparation of living polymers. The disclosurein this patent is identical to that of the '034 patent, as the '880patent is a continuation of the '034 patent, and therefore, does notbear repeating herein.

The essence of the disclosures in the above mentioned patents issummarized in a publication in Macromolecules 1984, 17, 1415 to 1417.This publication is important because it sets forth the details of thecatalysts that have been found useful by the above-mentioned patentees.Thus, the article sets forth at page 1416, left hand column, at thebottom, that the catalysts have to be used at levels of about 10 to 20mol % relative to monomer to achieve complete conversions of acrylatesand methacrylates.

THE INVENTION

The present invention relates to a method of controlling thepolymerization of acrylates using a novel catalyst which is selectedfrom at least one of a zinc, cadmium, or mercury halide, in combinationwith free iodine to give acrylate polymers having narrow molecularweight distributions via group transfer polymerization.

More specifically, the present invention relates to a method of grouptransfer polymerization to produce living polymers from acrylic-typemonomers and the novel catalysts.

Thus, the present invention comprises in one embodiment, a method ofcontrolling the polymerization of acrylates, the method comprising (I)contacting an initiator, one or more acrylic monomers and, a catalyst,for a time sufficient and at a temperature sufficient to create apolyacrylate polymer selected from the group consisting essentially ofpolyacrylate homopolymers and polyacrylate co-polymers. The catalystsare selected from a group comprising a mixture of at least one compoundselected from Zn, Cd, and Hg halides, mixed with I₂.

In a further embodiment, the reaction is quenched after the desiredpolyacrylate polymer is formed.

Further, this invention includes the novel catalysts as compositions ofmatter, along with the polymers that are prepared by the methodsdisclosed and claimed herein.

With regard to the invention herein, the term "living" polymer means apolymer of the invention which contains an active terminal group and iscapable of polymerizing further in the presence of monomers andcatalyst.

It has been discovered that by combining free iodine with the Lewis acidhalides described above, a process is provided which gives polymershaving narrow molecular weight distributions, higher molecular weights,and nearly one hundred percent of conversion of the starting monomers.

The process contemplates the contacting of the reactants, that is, amonomer, or mixture of monomers, and an initiator, with the catalyst,heating the reaction at a temperature and for a period of time toconvert essentially all of the monomer to polymer.

Thus, the monomeric reactants useful in this method are those acrylatemonomers which are suitable for use in this type of reaction andinclude, but are not limited to those set forth in the '034 patent, saidpatent being incorporated herein by reference for what it teaches aboutsuch monomers, it being understood by those skilled in the art that thisinvention does not deal with, nor include methacrylate monomers.

More specifically, the monomers include methyl acrylate; butyl acrylate;sorbyl acrylate; ethyl acrylate; propargyl acrylate;2-(dimethylamino)ethyl acrylate; 3,3-dimethoxypropyl acrylate;3-methacryloxypropyl acrylate; 2,2,3,3,4,4,4-heptafluorobutyl acrylate;ethyl 2-cyanoacrylate; 4-fluorophenyl acrylate; 2-methacryloxyethylacrylate; ethyl 2-chloroacrylate; phenyl acrylate;2{(1-propenyl)oxy}ethyl acrylate; and allyl acrylate. Preferred monomersinclude methyl acrylate; ethyl acrylate; butyl acrylate; sorbylacrylate; 2-methacryloxyethyl acrylate; propargyl acrylate and neopentylglycol diacrylate. Methyl acrylate, propargyl acrylate, and neopentylglycol diacrylate are the most preferred.

Initiators which are useful in the inventive process herein arewell-known in the art and reference can be made to several U.S. patentsfor examples of such initiators, for example, U.S. Pat. Nos. 4,754,046,5,208,358, 4,783,543, and 5,247,112, to name a few. The initiators setforth in the aforementioned U.S. patents dealing with initiators arehereby incorporated by reference to show the range and type ofinitiators useful in this invention.

More specifically, initiators useful in this invention include silanessuch as {(1-methoxy-2-methyl-1-propenyl)oxy}trimethyl-silane;2-(trimethylsilyl)isobutyronitrile;ethyl 2-(trimethylsilyl) acetate;trimethylsilyl nitrile; ((4,5-dihydro-2-2-furanyl)oxy}trimethylsilane;{(2-methyl-1-propenylidene)bis(oxy)} bis{trimethylsilane};{(2-methyl-1-{2-(methoxmethoxy)ethoxy}-1-propenyl)oxy}trimethylsilane;methyl {(2 -methyl-1-(trimethylsilyloxy)-1-propenyl)oxy}acetate, and thelike.

The ratio of the initiator to the monomer will determine the molecularweight of the polymer. Low levels of initiator give higher molecularweights. Too much initiator will give mostly oligomeric materials. Thus,the initiator is employed at a concentration such that the monomer toinitiator molar ratio is greater than 10, preferably greater than 100.

The monomers and initiators useful in this process are generally liquidsand can be polymerized without a solvent, although a solvent isbeneficial in controlling temperature during exothermic polymerizationwhich is common with this type of reaction. A solvent has been founduseful in the method of this invention and suitable solvents are aproticliquids in which the monomer, initiator and catalyst are sufficientlysoluble for the reaction to occur. Thus, such solvents include toluene,xylene, the so-called crown ethers, acetonitrile, tetrahydrofuran, ethylacetate, propionitrile, bromobenzene, dimethoxyethane, diethoxyethane,diethylether, tetramethylenesulfone, N,N-dimethylformamide,N,N-dimethylacetamide, N-methylpyrrolidone, anisole,2-butoxyethoxytrimethylsilane, other low boiling silanes, and the like.Preferred are toluene and xylene.

When a solvent is used, the monomer may be dissolved therein atconcentrations of at least five (5) weight percent, preferably at leastfifty (50) weight percent.

The time that the reaction can be run varies from a few minutes to a fewdays, depending on the temperature at which the reaction is carried out.The reaction is normally carried out within a few hours and quite often,the reaction is essentially complete in minutes. The temperature rangefor the reaction of this method is 0° to 80° C. Preferred is atemperature range of to 25° C to 40° C.

The catalyst, which is the essential feature of this invention, isformed from halides of zinc, cadmium, or mercury. Preferred for thisinvention are the iodides and bromides and nost preferred are theiodides. It is essential for the halides of this invention to becombined with free iodine, i.e. I₂ in order to form the catalyst of thisinvention. It is contemplated within the scope of this invention to usemixed halides with the iodine. The useful molar ratio of zinc, cadmium,or mercury halide to I₂ is on the order of at least 1.25:1 to less than19:1. However, it is preferred that the ratio be less than 15 to 1. Mostpreferred for this invention is the combination of zinc iodide with freeiodine in a ratio of 10 to 1.

The catalyst is normally present in such an amount that the molar ratioof monomer to catalyst is in the range of 0.04 parts of catalyst to 100parts of monomer, and is preferably in the range of 0.08 or higher, to100 parts of monomer.

The order of addition of the monomers, initiator and catalyst iscritical for this invention. For example, one should not add the I₂ tothe initiator because they react with each other in the absence of metalhalide. This, of course deactivates the initiator. More specifically,initiator can be decomposed by I₂ in the absence of metal halide. Thus,the preferred method is the addition of the initiator as quickly as ispossible to a combination of the monomers and catalyst in the reactionvessel.

The solvent, if used, can be added at any stage, but is preferably addedat the beginning of the reaction, before any addition of initiator takesplace.

Upon determining that the reaction has essentially been completed, forexample, by showing the absence of any monomer in the reaction mass, thereaction can be stopped, i.e. quenched, by the addition of any activehydrogen source such as water, or alcohol. Preferred for this inventionare lower alcohols such as methyl, ethyl, propyl, butyl, amyl, and thelike, and most preferred is methyl alcohol.

This invention is useful for preparing homopolymers or copolymers of themonomers described above. With this invention, it is possible to createvariation in polymer physical properties, such as glass transitiontemperature, hardness, heat distortion temperature, and melt viscosity.

The process of this invention can be used to prepare polymers containingone or more specifically located functional groups which are useful forsubsequent preparation of block copolymers or crosslinked polymers andthe details of such materials as found in U.S. Pat. No. 4,417,034 isincorporated herein by reference for what it teaches about thosematerials.

Now so that those skilled in the art can appreciate the scope and valueof the invention the following examples are provided.

EXAMPLE 1 Preparation of a Polymer by the Method of This Invention

This example illustrates the molecular weight distribution of thepolymers prepared by one embodiment of the instant invention.

A catalyst was made by mixing 10 weight parts of ZnI₂ with one weightpart of iodine. To a glass, round-bottomed, three-necked flask, equippedwith a magnetic stirrer was loaded 0.02 grams of the catalyst, 20 gramsof methyl acrylate, and 20 grams of toluene. The mixture was purple incolor at this point. The flask was cooled in a water bath. Uponstirring, 1.0 gram of ##STR1## addition. The purple color disappearedimmediately after the introduction of the silane. After a very shortinduction period, an exothermic reaction was observed by touching theflask. The mixture was allowed to stir at room temperature overnight andthen quenched with methanol. As methanol was added, a brownish purplecolor reappeared. The product mixture was washed with ten percent sodiumthiosulfate twice, followed by water twice, then dried over sodiumsulfate. Toluene and other volatiles, if any, were removed under reducedpressure to obtain a slightly yellowish viscous, clear polymer. GPCanalysis with THF as the mobile phase (0.35 weight percent/volume) andpolystyrene as the Standard gave the molecular weight data found inTable I.

                  TABLE I                                                         ______________________________________                                        RESULTS OF GPC ANALYSIS                                                       ______________________________________                                        Mn = 8825          Mw/Mn = 1.052                                              Mw = 9286          Mz/Mw = 1.045                                              Mz = 9701          Mz/Mn = 1.099                                              ______________________________________                                    

EXAMPLE 2

A second polymer was made by making a catalyst by mixing nine weightparts of ZnI₂ with one weight part of iodine. To a flask equipped as setforth above, was added 0.02 grams of the catalyst, 2.0 grams of methylacrylate, and 20 grams of toluene. The mixture was purple in color. Uponstirring at room temperature, the silane as was used in example 1 wasadded at a 1.0 gram level. The purple color disappeared immediatelyafter the introduction of the silane. To the reaction flask was thenadded 2.5 grams of propargyl acrylate, followed by 18.0 grams of methylacrylate. The reaction mixture became warm (about 45° C.). The mixturewas allowed to stir at room temperature overnight (about 16 hrs.) andthen quenched with methanol. Toluene, and other volatiles if any, wereremoved under reduced pressure to obtain a viscous, clear polymer. GPCanalysis with THF as the mobile phase (0.25 weight percent/volume) andpolystyrene as the Standard gave the following molecular weight data.

                  TABLE II                                                        ______________________________________                                        RESULTS OF GPC ANALYSIS                                                       ______________________________________                                        Mn = 10720         Mw/Mn = 1.197                                              Mw = 12830         Mz/Mw = 1.145                                              Mz = 14690         Mz/Mn = 1.371                                              ______________________________________                                    

An IR spectrum showed the polymer contained functional groups of C═O(1787 CM-1) and a carbon to carbon triple bond (2133 cm-1). No carbon tocarbon double bond signal for the acrylic functionality was observed byIR.

EXAMPLE 3

Several runs were carried out to examine several variables byessentially the procedure as set forth above in examples 1 and 2.

Table III has the results of the runs.

EXAMPLE 4 Criticality of not adding I₂ to the Initiator

(Treatment of sample 2 of this example falls outside of the scope ofthis invention.)

A reaction was carried out using the material of sample 1 wherein, itwill be noted, there was no free iodine present in the catalyst. Thissample was subjected to 10 minutes of aging, and then 0.4 parts of freeiodine was added to the mixture. Before the addition of the iodine, andduring the aging period, there was no reaction. However, upon theaddition of the free iodine, the material instantly polymerized.

Sample 2, having no ZnI₂, was aged for 10 minutes in the presence of thefree iodine and then 2 parts of ZnI₂ was added. There was no reactionwithin a thirty minute time period. It is believed that the contact ofthe free iodine with the initiator in the reactants deactivated theinitiator.

                                      TABLE III                                   __________________________________________________________________________    RESULTS OF VARIABLES EXAMINATION                                              SAMPLE                                                                              AMT. OF                                                                             RATIO                                                                              CATALYST/100                                                                             MONOMER                                           NUMBER                                                                              MI2/I2                                                                              X:1  PARTS MONOMER                                                                            TYPE*  OBSERVATION                                __________________________________________________________________________    1     2/0   0    2.0        NPGDA  No react./10 min.                          2       0/0.8                                                                             0    .8         NPGDA  No react./10 min.                           3*   0.19/0.01                                                                           19   0.2        NPGDA  No react./48 hr.                           4     1.8/0.2                                                                             9    2.0        NPGDA  Instant polymer.                           5     1.8/0.2                                                                             9    2.0        MA     Instant polymer.                           6     0.033/0.007                                                                         4.7  0.0        NPGDA  Polymeriz./2-4 hr                          7     0.164/0.036                                                                         4.6  0.2        "      Instant polymer.                           8     0.030/0.010                                                                         3    0.0        "      Polymeriz./2-4 hr                          9     0.149/0.051                                                                         2.9  0.2        "      Instant polymer.                           10    0.029/0.011                                                                         2.6  0.0        "      Polymeriz/2-16 hr                          11    0.143/0.057                                                                         2.5  0.2        "      Instant polymer.                           12    0.027/0.013                                                                         2.1  0.0        "      Polymeriz./2-4 hr                          13    0.134/0.066                                                                         2.0  .2         "      Instant polymer.                           14    0.111/0.089                                                                         1.25 0.2        "      Instant polymer.                           15    0.022/0.018                                                                         1.22 0.0        "      No react./48 hr.                           __________________________________________________________________________     *NPDGA is Neopentyl glycol Diacrylate                                         MA is methyl acrylate                                                    

EXAMPLE 5

A reaction was carried out at room temperature using 100 grams ofneopentyl glycol diacrylate, 5 grams of the initiator of example 1, and0.9 grams of ZnBr2/I2 in the ratio of 1.25:1. The reactants polymerized,but slower than those of examples 1 and 2.

EXAMPLE 6

A reaction was carried out at room temperature using 100 grams ofneopentyl glycol diacrylate, 5 grams of the initiator of example 1, and1.0 gram of HgBr2/I2 in the ratio of 1.56:1. The reactants polymerized,but slower than those of examples 1 and 2.

That which is claimed is:
 1. A method of preparing a polyacrylate polymer, said method comprising(I) contacting and reactingA. an initiator and B. one or more acrylic monomers in the presence of C. a catalyst,for a time sufficient and at a temperature sufficient to create a polyacrylate polymer, said polymer selected from the group consisting essentially of i polyacrylate homopolymers and ii polyacrylate co-polymers, said catalyst being a mixture of at least one metal halide compound selected from Zn, Cd and Hg halides, mixed with I₂, and (II) quenching the reaction after the desired polyacrylate polymer is formed, and (III) recovering the polyacrylate polymer from II. 